This invention relates to electrical control circuitry. More particularly, it involves a servo system for maintaining constant tension on a film or web during movement thereof.
There are many applications in which it is desirable, if not imperative, to maintain constant tensioning on a web during movement between one reel to another. In the past, this has been accomplished through somewhat complex servo systems utilizing spring biased buffer loops, capstans, clutches, etc. Unfortunately, these systems have tended to be difficult to implement and maintain, as well as unduly increasing the cost of the product in which they are utilized.
In the referenced patent recited above, a reproduction machine is disclosed in which copies are made from original documents in the form of image transparencies on a film. The film contains a plurality of documents in a preselected coded arrangement which can be individually addressed, or copied in sequence as desired. The film may be part of a reel to reel cassette, with the cassette being mounted in the exposure station of the machine. When a copy is desired of a particular original, the operator programs machine to move the film and position the desired original on the platen for making copies. The goal of present day reproduction machines is not only to provide good copy quality but also to be capable of producing large numbers of copies in a given amount of time. Consequently, the throughput of the machine depends upon how fast the machine can position the desired original on the platen. Consequently, it is of paramount importance in machines utilizing an automatic document handler such as that described in the Donohue patent that constant tension be maintained on the film during such positioning, e.g. so that the document lies flat against the platen during exposure.